1. Field of the Invention
The present invention relates to an ultrasonic diagnosis apparatus which is applied to a diagnosis using an ultrasonic contrast medium.
2. Description of the Related Art
An ultrasonic diagnosis apparatus radiates ultrasonic pulses into a living body, receives waves reflected by a boundary surface between tissues having different specific acoustic impedances (products of the densities of the two media and the sonic speed), and acquires an image by processing the received waves. The ultrasonic diagnosis apparatus does not cause an exposure trouble unlike in an X-ray diagnosis method, and is a clinically effective apparatus. In addition, along with the advance of various kinds of techniques such as an electron scanning technique, real-time performance has been improved, and moving object measurement has become easier.
In recent years, as the development of an ultrasonic contrast medium progresses, expectations for a close blood-flow diagnosis equivalent to X-ray angiography have been keen. The ultrasonic contrast medium has a clearly different nature in a reception signal from a living body and its intensity. With this medium, since a portion into which an ultrasonic contrast medium flows has a different luminance or gradation level from that of other portions on a B-mode image, an observer can observe the flow-in state of the ultrasonic contrast medium.
visual observation of the flow-in state of the ultrasonic contrast medium can only provide very low accuracy. In order to improve diagnostic accuracy, various kinds of information such as a change, over time, in flow-in/out amount of a contrast medium in/from a region of interest, its rise time, and the like are required. Conventional ultrasonic diagnosis apparatuses cannot provide such kinds of information. For this reason, an observer measures the total density in a region of interest in units of frames, summarizes the measurement results in a graph, and uses the graph in diagnosis. As described above, in order to acquire various kinds of information, an observer is required to perform troublesome and time-consuming operations. In addition, such information cannot be obtained in real time. Furthermore, since a reception signal includes a living body component and a contrast medium component, the contrast medium component must be extracted from the reception signal in order to accurately measure the flow-in/out amount of the contrast medium in/from a region of interest. However, ultrasonic waves are influenced more easily by motions of a living body portion than X-rays, and their intensity is unstable over time even for a living body component of the same living body portion. For this reason, it is difficult to accurately extract the contrast medium component from the reception signal.
The dynamic range of a normal ultrasonic diagnosis apparatus is set to be an expected intensity width of a reception signal from living body tissues in order to increase contrast. For this reason, since the contrast medium component in the reception signal has a clearly different intensity from that of a reception signal from a living body, it may be saturated beyond the upper limit of the dynamic range. For this reason, image formation is often disabled.
Furthermore, it is effective to simultaneously observe two separate portions, e.g., the carotid artery and an internal vein in acquisition of the flow-in state of the contrast medium. For this reason, conventionally, two ultrasonic diagnosis apparatuses are used. However, beat noise components are generated in acquired images of each apparatus due to the influence of ultrasonic waves of the other apparatus. In addition, since the two apparatuses independently generate images, they have different standard signal levels due to differences of the electric/ultrasonic conversion characteristics of their probes, the gain characteristics of preamplifiers, and the like, and hence, the images acquired by the two apparatuses cannot be compared with each other.